Source : Webster's Revised Unabridged Dictionary (1913)

Stain \Stain\, v. t. [imp. & p. p. {Stained}; p. pr. & vb. n.
   {Staining}.] [Abbrev. fr. distain.]
   1. To discolor by the application of foreign matter; to make
      foul; to spot; as, to stain the hand with dye; armor
      stained with blood.

   2. To color, as wood, glass, paper, cloth, or the like, by
      processess affecting, chemically or otherwise, the
      material itself; to tinge with a color or colors combining
      with, or penetrating, the substance; to dye; as, to stain
      wood with acids, colored washes, paint rubbed in, etc.; to
      stain glass.

   3. To spot with guilt or infamy; to bring reproach on; to
      blot; to soil; to tarnish.

            Of honor void, Of innocence, of faith, of purity,
            Our wonted ornaments now soiled and stained.
                                                  --Milton.

   4. To cause to seem inferior or soiled by comparison.

            She stains the ripest virgins of her age. --Beau. &
                                                  Fl.

            That did all other beasts in beauty stain.
                                                  --Spenser.

   {Stained glass}, glass colored or stained by certain metallic
      pigments fused into its substance, -- often used for
      making ornament windows.

   Syn: To paint; dye; blot; soil; sully; discolor; disgrace;
        taint.

   Usage: {Paint}, {Stain}, {Dye}. These denote three different
          processes; the first mechanical, the other two,
          chiefly chemical. To paint a thing is so spread a coat
          of coloring matter over it; to stain or dye a thing is
          to impart color to its substance. To stain is said
          chiefly of solids, as wood, glass, paper; to dye, of
          fibrous substances, textile fabrics, etc.; the one,
          commonly, a simple process, as applying a wash; the
          other more complex, as fixing colors by mordants.

Source : WordNet®

staining
     n 1: (histology) the use of a dye to color specimens for
          microscopic study
     2: the act of spotting or staining something [syn: {spotting},
        {maculation}]